Semiconductor device, display device, and method for manufacturing the same

ABSTRACT

Provided is a semiconductor device including: a first transistor over a substrate, the first transistor having a gate electrode, an oxide semiconductor film, and a gate insulating film between the gate electrode and the oxide semiconductor film; an insulating film over the first transistor, the insulating film having a first film and a second film over the first film; and a terminal electrically connected to the oxide semiconductor film through an opening portion in the insulating film. The insulating film has a first region in contact with the terminal, and the first region has an oxygen composition larger than that in another region of the insulating film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from theprior Japanese Patent Application No. 2016-063238, filed on Mar. 28,2016, the entire contents of which are incorporated herein by reference.

FIELD

An embodiment of the present invention relates to a semiconductordevice, a display device having the semiconductor device, and amanufacturing method thereof.

BACKGROUND

As a typical example exhibiting semiconductor properties, Group 14elements such as silicon and germanium are represented. Particularly,silicon has been utilized in almost all semiconductor devices andrecognized as a material supporting the basis of the electronicsindustry because of its wide availability, easiness of processing,excellent semiconductor properties, and easiness of controllingproperties.

Recent finding of semiconductor properties in oxides, in particularoxides of Group 13 elements such as indium and gallium, has motivatedintensive research and development. As a typical example of oxidesexhibiting semiconductor properties (hereinafter, referred to as anoxide semiconductor), indium-gallium oxide (IGO), indium-gallium-zincoxide (IGZO), and the like have been known. Intensive research in recentyears has realized commercialization of display devices havingtransistors including these oxide semiconductors as a semiconductorelement. Additionally, as exemplarily disclosed in Japanese patentapplication publication No. 2015-225104, international publication No.2015-031037, and United States patent application publication2010/0182223, a semiconductor device in which both a transistor having asilicon-including semiconductor (hereinafter, referred to as a siliconsemiconductor) and a transistor having an oxide semiconductor areincorporated has been developed.

SUMMARY

An embodiment of the present invention is a semiconductor deviceincluding: a first transistor over a substrate, the first transistorhaving a gate electrode, an oxide semiconductor film, and a gateinsulating film between the gate electrode and the oxide semiconductorfilm; an insulating film over the first transistor, the insulating filmhaving a first film and a second film over the first film; and aterminal electrically connected to the oxide semiconductor film throughan opening portion in the insulating film. The insulating film has afirst region in contact with the terminal, and the first region has anoxygen composition larger than that in another region of the insulatingfilm.

An embodiment of the present invention is a display device including: afirst transistor over a substrate, the first transistor having a gateelectrode, an oxide semiconductor film, and a gate insulating filmbetween the gate electrode and the oxide semiconductor film; aninsulating film over the first transistor, the insulating film having afirst film and a second film over the first film; a terminalelectrically connected to the oxide semiconductor film through anopening portion in the insulating film; a leveling film over theterminal; and a display element over the leveling film. The insulatingfilm has a first region in contact with the terminal, and the firstregion has an oxygen composition larger than that in another region ofthe insulating film.

An embodiment of the present invention is a manufacturing method of asemiconductor device. The manufacturing method includes: forming a firsttransistor over a substrate, the first transistor having a gateelectrode, an oxide semiconductor film, and a gate insulating filmbetween the gate electrode and the oxide semiconductor film; forming aninsulating film having a first film and a second film over the firstfilm; forming an opening portion in the insulating film; oxidizing theinsulating film so that a surface portion of the opening portion has afirst region with an oxygen composition larger than that in anotherregion; and forming a terminal in the opening portion so as to beelectrically connected to the oxide semiconductor film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A and FIG. 1B are respectively a schematic cross-sectional viewand an oxygen-composition profile of a semiconductor device of anembodiment of the present invention;

FIG. 2A to FIG. 2D are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 3A to FIG. 3D are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 4A to FIG. 4C are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 5A is a schematic cross-sectional view and an oxygen-compositionprofile of a semiconductor device of an embodiment of the presentinvention;

FIGS. 5B and 5C are oxygen-composition profiles of a semiconductordevice of an embodiment of the present invention;

FIG. 6A to FIG. 6C are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 7A and FIG. 7B are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 8 is a schematic cross-sectional view of a semiconductor device ofan embodiment of the present invention;

FIG. 9A to FIG. 9C are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 10A to FIG. 100 are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 11A and FIG. 11B are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 12A and FIG. 12B are schematic cross-sectional views showing amanufacturing method of a semiconductor device of an embodiment of thepresent invention;

FIG. 13 is a schematic top view of display devices of embodiments of thepresent invention;

FIG. 14 is an equivalent circuit of a pixel of a display device of anembodiment of the present invention;

FIG. 15 is a schematic cross-sectional view of a display device of anembodiment of the present invention;

FIG. 16 is a schematic cross-sectional view of a display device of anembodiment of the present invention;

FIG. 17 is a schematic cross-sectional view of a display device of anembodiment of the present invention; and

FIG. 18 is a schematic cross-sectional view of a display device of anembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the embodiments of the present invention are explained withreference to the drawings. The invention can be implemented in a varietyof different modes within its concept and should not be interpreted onlywithin the disclosure of the embodiments exemplified below.

The drawings may be illustrated so that the width, thickness, shape, andthe like are illustrated more schematically compared with those of theactual modes in order to provide a clearer explanation. However, theyare only an example, and do not limit the interpretation of theinvention. In the specification and the drawings, the same referencenumber is provided to an element that is the same as that which appearsin preceding drawings, and a detailed explanation may be omitted asappropriate.

In the present invention, when a plurality of films is formed byprocessing one film, the plurality of films may have functions or rulesdifferent from each other. However, the plurality of films originatesfrom a film which is formed as the same layer in the same process.Therefore, the plurality of films is defined as films existing in thesame layer.

In the specification and the claims, unless specifically stated, when astate is expressed where a structure is arranged “over” anotherstructure, such an expression includes both a case where the substrateis arranged immediately above the “other structure” so as to be incontact with the “other structure” and a case where the structure isarranged over the “other structure” with an additional structuretherebetween.

First Embodiment

In the present embodiment, a semiconductor device according to anembodiment of the present invention is explained by using FIG. 1A toFIG. 4C.

1. Structure

A schematic cross-sectional view of a semiconductor device 100 which isa semiconductor device according to the present embodiment is shown inFIG. 1A. The semiconductor device 100 has a first transistor 102 over asubstrate 104 with an undercoat 106 interposed therebetween. The firsttransistor 102 includes a gate electrode 108, an oxide semiconductorfilm 112, and a gate insulating film 110 sandwiched by the gateelectrode 108 and the oxide semiconductor film 112. The first transistor102 further contains source/drain electrodes 114 and 116 over andelectrically connected to the semiconductor film 112. In the presentspecification, a transistor means a structure including a gateelectrode, an oxide semiconductor, a gate insulating film, and a pair ofsource/drain electrodes, and another element may be included in theseelements.

The semiconductor device 100 further possesses an interlayer film 120over the first transistor 102 so as to cover the semiconductor film 112and the source/drain electrodes 114 and 116. The interlayer film 120 isan insulating film and has three films (first film 112, second film 124,and third film 126) in the present embodiment. A first terminal 128 anda second terminal 130 passing through the interlayer film 120 areprovided in the semiconductor device 100 and electrically connected tothe source/drain electrodes 114 and 116, respectively. The semiconductordevice 100 may contain a leveling film 132 as an optional structure, anda variety of semiconductor elements exemplified by a display element maybe formed over the leveling film 132.

As shown in an enlarged figure of FIG. 1A (a portion surrounded by acircle in the drawing), first regions 140 are formed in the interlayerfilm 120. The first regions 140 are in contact with a surface of theinterlayer film 120 and spread inside from the surface of the interlayerfilm 120. More specifically, the first regions 140 are included in thesecond film 124 of the interlayer film 120, and the first terminal 128and the second terminal 130 are in contact with the first regions 140.Therefore, the first regions 140 are formed so as to surround the firstterminal 128 and the second terminal 130. An oxygen composition of thefirst regions 140 is larger than that of another region of the secondfilm 124.

The first regions 140 can have a composition profile in which the oxygencomposition decreases with increasing distance from the surface. Forexample, as schematically shown in FIG. 1B, the first regions 140 may beformed so that the oxygen composition decreases from an interfacebetween the first region 140 and the first terminal 128 or an interfacebetween the first region 140 and the second terminal 130 in a directionparallel to a top surface of the substrate 104 (a direction of an arrowX in the enlarged figure of FIG. 1A). The oxygen content may decreaselinearly as illustrated by a solid straight line 142 or decrease in acurve as represented by curves 143 and 144. In the case where the oxygencontent decreases in a curve, it may decrease exponentially. Note that aregion of the interlayer film 120 other than the first regions 140(i.e., another region) is a region in which the oxygen composition issubstantially constant even if the distance from the surface increasesand corresponds to a region expressed by a dotted straight line in FIG.2B. The oxygen composition of the interlayer film 120 can be estimatedby a secondary ion mass spectroscopy (SIMS) and the like, for example.

In FIG. 1A, the so-called bottom gate-top contact type first transistor102 is shown as an example. However, the mode of the present embodimentis not limited thereto, and a variety of structures can be employed. Forexample, the first transistor 102 may be a top-gate type transistor, andany of a top-contact type and a bottom-contact type may be applied withrespect to the up-and-down relationship between the source/drainelectrodes 114 and 116 and the oxide semiconductor film 112. In the caseof the top-gate type, the first transistor 102 may have a so-calledself-align structure. In the case of the bottom-gate type, the firsttransistor 102 may have a so-called channel-etch type structure in whicha channel region of the oxide semiconductor film 112 is thinner than theregions covered by the source/drain electrodes 114 and 116.Alternatively, the first transistor 102 may have a so-calledchannel-stop type structure having an insulating film between the oxidesemiconductor film 112 and the source/drain electrodes 114 and 116. Thefirst transistor 102 may not necessarily possess only a single gateelectrode 108 and may be a multi-gate transistor having two or more gateelectrodes.

2. Manufacturing Method

A manufacturing method of the semiconductor device 100 is explained withreference to FIG. 2A to FIG. 4C.

2-1. Substrate

First, the undercoat 106 is formed over the substrate 104 (FIG. 2A). Thesubstrate 104 has a function to support the first transistor 102 and avariety of semiconductor elements formed over the leveling film 132.Hence, a material having heat resistance to a process temperature of thevariety of elements formed thereover and chemical stability to chemicalsused in the process may be used for the substrate 104. Specifically, thesubstrate 104 may contain glass, quartz, plastics, a metal, ceramics,and the like. When flexibility is provided to the semiconductor device100, a polymer material can be used. For example, a polymer materialexemplified by a polyimide, a polyamide, a polyester, a polycarbonatecan be employed. Note that, in the case of fabricating the semiconductordevice 100 with flexibility, the substrate 104 may be called a basematerial or a base film.

2-2. Undercoat

The undercoat 106 is a film having a function to prevent impurities suchas alkaline metal ions from diffusing from the substrate 104 to thefirst transistor 102 and the like and may include an inorganic insulatorsuch as silicon nitride, silicon oxide, silicon nitride oxide, andsilicon oxynitride. The undercoat 106 can be formed so as to have asingle-layer or stacked-layer structure by applying a chemical vapordeposition method (CVD method), a sputtering method, a laminationmethod, and the like. When a CVD method is used, a tetraalkoxysilane andthe like may be used as a raw-material gas. A thickness of the undercoat106 can be freely selected from a range from 50 nm to 1000 nm, and isnot necessarily constant over the substrate 104. The undercoat 106 mayhave different thicknesses depending on position. When the undercoat 106is structured with a plurality of layers, a layer including siliconnitride is stacked over the substrate 104 and a layer including siliconoxide is stacked thereover.

Note that when an impurity concentration of substrate 104 is low, theundercoat 106 may not be formed or may be formed so as to partly coverthe substrate 104. For example, when a polyimide with a lowconcentration of alkaline metal ions is used, the gate electrode 108 maybe formed so as to be in contact with the substrate 104 without theformation of the undercoat 106.

2-3. Gate Electrode

Next, the gate electrode 108 is formed over the undercoat 106 (FIG. 2B).The gate electrode 108 can be formed so as to have a single-layer orstacked layer structure by using a metal such as titanium, aluminum,copper, molybdenum, tungsten, and tantalum or an alloy thereof. When thesemiconductor device 100 of the present embodiment is applied to, forexample, a large-area semiconductor device such as a display device, itis preferred to use a metal with high conductivity, such as aluminum andcopper, in order to prevent signal delay. For instance, a structure inwhich aluminum or copper is sandwiched by a metal with a relatively highmelting point, such as titanium and molybdenum, can be applied.

2-4. Gate Insulating Film

Next, the gate insulating film 110 is formed over the gate electrode 108(FIG. 2B). The gate insulating film 110 may have any of a single-layerstructure and a stacked-layer structure and can include an inorganicinsulator exemplified by silicon oxide, silicon nitride, siliconoxynitride, and silicon nitride oxide. It is particularly preferred touse an insulating film containing silicon oxide as the gate insulatingfilm 110 in order to suppress carrier generation in the oxidesemiconductor film 112. The gate insulating film 110 can be formed byapplying a sputtering method, a CVD method, or the like. It is preferredthat the atmosphere during the film-formation contain ahydrogen-containing gas such as hydrogen gas and vapor as little aspossible, by which the gate insulating film 110 having a small hydrogencomposition and an oxygen composition close to or larger than that ofstoichiometry.

2-5. Oxide Semiconductor Film

Next, the oxide semiconductor film 112 is formed over the gateinsulating film 110 (FIG. 2C). The oxide semiconductor film 112 maycontain Group 13 elements such as indium and gallium. The oxidesemiconductor film 112 may include a plurality of different Group 13elements and may be a mixed oxide of indium and gallium (IGO). The oxidesemiconductor film 112 may further contain Group 12 elements, and amixed oxide including indium, gallium, and zinc is represented as anexample. The oxide semiconductor film 112 may contain another elementsuch as tin of Group 14 elements, and titanium and zirconium of Group 4elements. There is also no limitation to crystallinity of the oxidesemiconductor film 112, and the oxide semiconductor film 112 may besingle-crystalline, polycrystalline, microcrystalline, or amorphous. Itis preferred that the oxide semiconductor film 112 possess a smallnumber of crystal defects such as an oxygen defect.

The oxide semiconductor film 112 is formed at a thickness of 20 nm to 80nm or 30 nm to 50 nm by utilizing a sputtering method and the like, andthen processed into a desired shape by patterning (etching). When asputtering method is applied, the film-formation may be carried outunder a mixed atmosphere of argon and oxygen gas, for example. In thiscase, a partial pressure of argon may be lower than that of oxygen gas.

A current applied to a target may be a direct current or an alternatingcurrent and can be determined depending on a shape, a composition, andthe like of the target. For example, a mixed oxide containing indium(In), gallium (Ga), and zinc (Zn) (In_(a)Ga_(b)Zn_(c)O_(d)) may be usedas a target. Here, a, b, c, and d are each a real number larger than 0and are not necessarily an integer. Hence, assuming that each elementexists as the most stable ion, the aforementioned composition is notalways an electrically neutral one. As an example of a targetcomposition, InGaZnO₄ is represented. However, the composition is notlimited thereto and may be selected as appropriate so that the oxidesemiconductor film 112 or the first transistor 102 including the oxidesemiconductor film 112 possesses the intended properties.

A heat treatment (annealing) may be performed on the oxide semiconductorfilm 112. The heat treatment may be carried out before or afterpatterning the semiconductor film 112. Since the oxide semiconductorfilm 112 may decrease in volume (shrinking) by the heat treatment, theheat treatment is preferably carried out before patterning. The heattreatment may be performed in the presence of nitrogen, dry air, or theatmosphere at an atmospheric or reduced pressure. The heatingtemperature can be selected from a range from 250° C. to 500° C. or from350° C. to 450° C., and the heating time can be selected from a rangefrom 15 minutes to 1 hour. However, the heat treatment may be carriedout outside these ranges. This heat treatment allows oxygen to beintroduced or migrate to the oxygen defects of the oxide semiconductorfilm 112, resulting in the more well-defined oxide semiconductor film112 with a smaller number of crystal defects and higher crystallinity.As a result, the first transistor 102 having excellent electricalproperties such as high reliability, a high on-current, a lowoff-current, and small variation in properties (threshold voltage) canbe obtained.

Although not illustrated, when the first transistor 102 has a top-gatestructure, for example, the semiconductor film 112 may be doped withimpurities so that the oxide semiconductor film 112 possessessource/drain regions in addition to a channel region overlapping withthe gate electrode 108. Crystal defects generated in the regions dopedwith the impurities increase conductivity and allow these regions tofunction as the source/drain regions.

2-6. Source/Drain Electrode

Next, the source/drain electrodes 114 and 116 are formed over the oxidesemiconductor film 112 (FIG. 2D). The source/drain electrodes 114 and116 can be formed by applying a material, a structure, and a formationmethod applicable to the gate electrode 108. When a channel-stop typetransistor is formed for example, an insulating film including siliconoxide may be formed over the oxide semiconductor film 112, and then thesource/drain electrodes 114 and 116 may be formed. Note that, a sourceand drain of a transistor may be interchanged depending on a polarity ofa transistor and a current direction. Therefore, the source/drainelectrodes 114 and 116 each may function as a source electrode and adrain electrode.

Through these processes, the first transistor 102 is formed.

2-7. Interlayer Film

Next, the interlayer film 120 is formed over the source/drain electrodes114 and 116. Here, the interlayer film 120 has the first film 122, thesecond film 124, and the third film 126, and the first film 122 is firstformed (FIG. 3A).

The first film 122 may contain a material usable in the undercoat 106and can be formed with a sputtering method or a CVD method. The firstfilm 122 may include aluminum oxide, chromium oxide, boron nitride, andthe like. The first film 122 is preferably an inorganic insulating filmwhich does not include nitrogen, and a silicon oxide film includingoxygen and silicon is given as an example. Similar to the formation ofthe gate insulating film 110, it is preferred that the atmosphere duringthe formation of the first film 122 contain a hydrogen-containing gassuch as hydrogen gas and vapor as little as possible, by which the firstfilm 122 having a small hydrogen composition and an oxygen compositionclose to or larger than that of stoichiometry can be formed.Accordingly, the first transistor 102 with stable and excellentelectrical properties can be obtained.

The second film 124 is formed over the first film 122 (FIG. 3B). Thesecond film 124 also may contain a material similar to that of the firstfilm 122 and can be formed with a method similar to that of the firstfilm 122. The second film 124 is preferred to include anitrogen-containing inorganic insulating material exemplified by siliconnitride containing nitrogen and silicon. The use of silicon nitrideenables impurities such as hydrogen and water which may be diffused froma variety of films formed thereover (e.g., leveling film 132 etc.) to beblocked, thereby reducing influence on the electrical properties of thefirst transistors 102. When silicon nitride is used in the second film124, a CVD method can be used in which ammonia or nitrogen oxide isutilized as a nitrogen source and a tetraalkoxysilane is employed as areaction gas. In this case, the film formation is preferably carried outby reducing a flow rate of a hydrogen-containing gas so that the secondfilm 124 has a small hydrogen composition in order to avoid influence onthe electrical properties of the transistor 102. Moreover, it ispreferred to perform the film formation at a relatively low temperature(equal to or higher than room temperature and equal to or lower than300° C., preferably equal to or higher than room temperature and equalto or lower than 200° C.).

The third film 126 is formed over the second film 124 (FIG. 3C). Thethird film 126 also may contain a material similar to that of the firstfilm 122 and can be formed with a method similar to that of the firstfilm 122. The third film 126 is preferred to include anoxygen-containing inorganic insulating material exemplified by siliconoxide containing oxygen and silicon. The interlayer film 120 is formedby stacking the first film 122, the second film 124, and the third film126.

Next, opening portions (contact holes) 118 exposing the source/drainelectrodes 114 and 116 are formed in the interlayer film 120 in order toform the first terminal 128 and the second terminal 130 (FIG. 3D). Theopening portions can be formed, for example, by performing plasmaetching in a gas including a fluorine-containing hydrocarbon.

After the formation of the opening portions 118, the first regions 140are formed by oxidizing a part of the interlayer film 120. For example,as shown in FIG. 4A, the oxidative treatment may be conducted byperforming an oxygen plasma treatment on the interlayer film 120.Specifically, the substrate 104 is placed between a pair of electrodes,and a high-frequency alternating voltage is applied between the pair ofelectrodes under an atmosphere including an oxygen-containing gas (e.g.,oxygen, ozone, etc.) to form a plasma. The frequency may be selectedfrom 13.56 MHz, 2.45 GHz, and the like. Accordingly, oxygen-containingions are fed to the surface of the interlayer film 120, and theinterlayer film 120 is oxidized.

The oxidation proceeds from the surface of the interlayer film 120 whichis collided with the oxygen-containing ions. Here, when the interlayerfilm 120 has a first film 122 containing silicon oxide, the second film124 containing silicon nitride, and the third film 126 containingsilicon oxide, for example, the first film 122 and the third film 126are relatively inactive to the oxidation because they originally containoxygen. On the other hand, the second film 124 exhibits activity to theoxidation because the second film 124 does not originally contain oxygenor contains oxygen at a relatively low composition. As a result, theoxidation proceeds in the second film 124 preferentially, resulting inthe formation of the first regions 140 in the second film 124.

The oxidation allows a part of nitrogen to be replaced with oxygen oroxygen to be trapped in the crystal defects and form a bond with siliconin the second film 124. Hence, the oxygen composition in the firstregions 140 formed by the oxidation is higher than that in a regionother than this region 140. These first regions 140 are formed so as tosurround the opening portions 118 (FIG. 4A). The first regions 140 arein contact with side surfaces of the opening portions 118 and spreadsinside from the surface of the interlayer film 120 because the oxidationproceeds from the surface of the interlayer film 120. In other words,the first regions 140 form a part of the side surfaces of the openingportions 118. Therefore, the oxygen composition of the first regions 140decreases with increasing distance from the surface of the interlayerfilm 120. In the case where the oxidation proceeds in the second film124 preferentially, the oxidation proceeds in a direction parallel to atop surface of the substrate 104 (the X direction in FIG. 1A). Thus, theoxygen composition decreases with increasing distance from the interfacewith the opening portions 118 in this direction. The oxygen compositiondecreases as illustrated in FIG. 1B, for example. Hence, the interfacebetween the first regions 140 and the region other than this region isnot always clearly observed in the second film 124.

Note that the oxidation may be conducted with a wet treatment instead ofthe plasma treatment. Specifically, the wet treatment is carried out bycontacting a solution including oxygen, ozone, or an oxidizer or vaporof oxygen-containing water with the interlayer film 120.

After the oxidative treatment is completed, an acid treatment may becarried out, by which oxide films formed over the source/drainelectrodes 114 and 116 by the plasma treatment can be removed. The acidtreatment can be conducted with a solution containing hydrogen fluoride,such as hydrofluoric acid, for example.

2.8 Terminal

After the oxidative treatment is completed, the first terminal 128 andthe second terminal 130 are formed so as to be in contact with thesource/drain electrodes 114 and 116, respectively (FIG. 4B). With thisprocess, the first terminal 128 and the second terminal 130 areelectrically connected to the source/drain electrodes 114 and 116,respectively, and make contact with the first regions 140. In theformation of the first terminal 128 and the second terminal 130, amaterial, a structure, and a formation method applicable to the gateelectrode 108 or the source/drain electrodes 114 and 116 can beemployed.

2-9. Leveling Film

After the formation of the first terminal 128 and the second terminal130, the leveling film 132 may be formed as an optional structure (FIG.4C). The leveling film 132 has a function to absorb projections,depressions, and inclinations caused by the first transistor 102 andprovide a flat surface. The leveling film 132 can be formed with anorganic insulator. As an organic insulator, a polymer material such asan epoxy resin, an acrylic resin, a polyimide, a polyamide, a polyester,a polycarbonate, and a polysiloxane, and the leveling film 132 can beformed with a wet-type film-formation method such as a spin-coatingmethod, an ink-jet method, a printing method, and a dip-coating method.The leveling film 132 may have a stacked structure including a layercontaining the aforementioned organic insulator and a layer containingan inorganic insulator. In this case, a silicon-containing inorganicinsulator such as silicon oxide, silicon nitride, silicon nitride oxide,and silicon oxynitride is represented as an inorganic insulator, and thelayer containing an inorganic insulator can be formed with a sputteringmethod or a CVD method. Through the aforementioned processes, thesemiconductor device 100 can be manufactured.

As described above, a function of the interlayer film 120 is to preventimpurities diffused from a variety of films (e.g., leveling film 132)formed over the first transistor 102 from entering the first transistor102. Therefore, it is preferred that the interlayer film 120 containsilicon nitride with low permeability to water and oxygen. On the otherhand, in the case where a film containing silicon nitride is formed, itis preferred to form the film at a reduced flow rate of thenitrogen-source gas including hydrogen at a relatively low temperature.However, when a film containing silicon nitride is formed under suchconditions, chemical stability is reduced and a part or all of the filmmay disappear when treated with an acid such as hydrofluoric acid, whichremarkably reduces the ability to block impurities. For example, when anacid treatment is conducted after the formation of the opening portions108, a part of the second film 124 may be lost by etching (side etching)with hydrofluoric acid.

However, as described above, when the semiconductor device 100 describedin the present embodiment is fabricated, the oxidative treatment isperformed on the interlayer film 120, by which the oxidation proceedsfrom the surface of the film containing silicon nitride (e.g., secondfilm 124) to form the first regions 140. With this process, the regionwith an increased oxygen composition is formed at the surface of thefilm containing silicon nitride, and the chemical stability is improved,by which side etching can be prevented even if an acid treatment iscarried out. As a result, the loss of the interlayer film 120 anddeterioration of its function can be avoided, allowing the production ofthe semiconductor device 100 with excellent electrical properties.

Second Embodiment

In the present embodiment, a semiconductor device according to anembodiment of the present invention and a manufacturing method thereofare explained by using FIG. 5A to 7B. Explanation of duplicated contentof the First Embodiment may be omitted.

1. Structure

A cross-sectional view of a semiconductor device 200 of the presentembodiment is shown in FIG. 5A. A difference from the semiconductordevice 100 is the structure of the interlayer film 120. The interlayerfilm 120 of the semiconductor device 200 has the first film 122 and thesecond film 124, and the second film 124 has first regions 150 at itstop surface and in a region in contact with the first terminal 128 orthe second terminal 130 and a region other than this region (secondregion) 152. The First Embodiment can be adopted with respect to thestructures other than this difference.

More specifically, the first film 122 corresponds to the first film 122of the First Embodiment and is a silicon-containing inorganic insulatingfilm including silicon oxide, silicon nitride, silicon oxynitride, andsilicon nitride oxide. The first film 122 is preferably a film whichcontains silicon oxide but does not contain nitrogen, and its smallhydrogen composition and an oxygen composition close to or larger thanthat of stoichiometry allows the formation of the first transistor 102with stable and excellent electrical properties.

The second film 124 is also an inorganic insulating film containing aninorganic insulator including silicon, such as silicon oxide, siliconnitride, silicon oxynitride, and silicon nitride oxide. The second film124 is preferably a film containing an inorganic insulator includingnitrogen and silicon, such as silicon nitride having high blockingability of impurities. The second film 124 has a function to preventimpurities from entering the first transistor 102.

The first regions 150 of the second film 124 spread from the top surfaceof the second film 124 and from an interface with the first terminal 128or the second terminal 130 and has a higher oxygen composition comparedwith that of the second region 152.

Similar to the first regions 140 of the semiconductor device 100 of theFirst Embodiment, the first regions 150 may have a composition profilein which the oxygen composition decreases with increasing distance fromthe surface. For example, as schematically shown in FIG. 5B, the firstregions 150 may be formed so that the oxygen composition decreases withincreasing distance from the interface between the first region 150 andthe first terminal 128 or the interface between the first region 150 andthe second terminal 130 in a direction (a direction of an arrow X inFIG. 5A) parallel to the top surface of the substrate 104. Similarly, asshown in FIG. 5C, the first regions 150 may be formed so that the oxygencomposition decreases with increasing distance from a top surface of thefirst regions 150 in a direction (a direction of an arrow Y in FIG. 5A)perpendicular to the top surface of the substrate 104. The oxygencomposition may decrease linearly as illustrated by solid straight lines142 and 146 or in a curve as represented by curves 143, 144, 147, and148. When the oxygen composition decreases in a curve, it may decreaseexponentially. The second region 152 is a region in which the oxygencomposition is substantially constant even if the distance from thesurface increases and corresponds to a region expressed by dotted linesin FIG. 5B and FIG. 5C.

2. Manufacturing Method

A manufacturing method of the semiconductor device 200 is explained withreference to FIG. 6A to FIG. 7B. Similar to the First Embodiment, thefirst transistor 102 is formed over the substrate 104 with the undercoat106 interposed therebetween, and then the interlayer film 120 is formed(FIG. 6A). The interlayer film 120 possesses the first film 122 and thesecond film 124 which correspond to the first film 122 and the secondfilm 124 of the First Embodiment, respectively. It is preferred that thefirst film 122 have silicon oxide including silicon and oxygen and thesecond film 124 have silicon nitride including silicon and nitrogen.

After the formation of the second film 124, the opening portions 118exposing the source/drain electrodes 114 and 116 are formed in theinterlayer film 120 in order to form the first terminal 128 and thesecond terminal 130 (FIG. 6B). As the formation method of the openingportions 118, the method described in the First Embodiment can be used.

After forming the opening portions 118, the oxidative treatment isperformed to oxidize a part of the interlayer film 120. The oxidativetreatment can be conducted similarly to that described in the FirstEmbodiment.

The oxidation proceeds from the surface of the interlayer film 120 whichis collided with oxygen-containing ions. Therefore, in the case wherethe interlayer film 120 has the first film 122 including silicon oxideand the second film 124 including silicon nitride, for example, thefirst film 122 is relatively inactive to the oxidation because the firstfilm 122 originally contains oxygen. On the other hand, the second film124 exhibits activity to the oxidation because the second film 124 doesnot originally contain oxygen or contains oxygen at a low composition.As a result, the oxidation proceeds preferentially in the second film124.

The oxidation allows a part of nitrogen to be replaced or oxygen to betrapped in the crystal defects and form a bond with silicon in thesecond film 124. Hence, the oxygen composition in the first regions 150formed by the oxidation is higher than that in the second region 152.The oxidation proceeds from the surface of the interlayer film 120.Therefore, the first regions 150 are formed not only at the top surfaceof the second film 124 and the vicinity thereof but also in a portion incontact with the side surfaces of the opening portions 118. Accordingly,the first regions 150 are in contact with the opening portions 118,surround the opening portions 118, spread from the surface of theinterlayer film 120, and form a part of the side surfaces of the openingportions 118 (FIG. 6C).

After that, similar to the First Embodiment, the first terminal 128 andthe second terminal 130 are formed in the opening portions 118 (FIG.7A). Furthermore, the leveling film 132 may be formed as an optionalstructure (FIG. 7B). Through the processes up to this stage, thesemiconductor device 200 is obtained.

In the manufacturing method of the semiconductor device 200 described inthe present embodiment, a part of the film (second film 124) which hashigh ability to block impurities but possesses low chemical stability isoxidized by performing the oxidative treatment. As a result, the film(first regions 150) having high chemical stability can be provided whileleaving the film (second region 152) having high ability to blockimpurities. Hence, it is possible to provide the interlayer film 120which is stable to an acid treatment such as a treatment withhydrofluoric acid and able to effectively block impurities, by which asemiconductor device with small variation in properties and excellentelectrical properties can be supplied.

Third Embodiment

In the present embodiment, a semiconductor device according to anembodiment of the present invention and a manufacturing method thereofare explained by using FIGS. 8 to 12B. Explanation of duplicatedcontents of the First Embodiment may be omitted.

1. Structure

A cross-sectional view of a semiconductor device 300 of the presentembodiment is shown in FIG. 8. The semiconductor device 300 possesses asecond transistor 160 and a third transistor 162 in addition to thefirst transistor 102 described in the First Embodiment. Although notshown, it is possible to dispose the first transistor 102 described inthe Second Embodiment instead of the first transistor 102 described inthe First Embodiment.

More specifically, the semiconductor device 300 has the undercoat 106over the substrate 104 and possesses the second transistor 160 and thethird transistor 162 so as to be in contact with the undercoat 106.

The second transistor 160 and the third transistor 162 havesemiconductor films containing silicon (hereinafter, referred to assilicon semiconductor film) 164 and 166, respectively, over which asecond gate electrode 170 and a third gate electrode 172 arerespectively provided with a second gate insulating film 168 sandwichedtherebetween. The second transistor 160 and the third transistor 162shown here each have a top-gate type self-align structure. However,similar to the first transistor 102 of the First Embodiment, the secondtransistor 160 and the third transistor 162 may possess a variety ofstructures.

The silicon semiconductor films 164 and 166 can include crystallinesilicon, polycrystalline silicon, microcrystalline silicon, or amorphoussilicon. Hereinafter, an embodiment is described as an example in whichthe silicon semiconductor films 164 and 166 include polycrystallinesilicon. As shown in FIG. 8, the silicon semiconductor films 164 and 166each have a channel region and source/drain regions. In the exampleshown in FIG. 8, the silicon semiconductor film 164 has a channel region164 a and source/drain regions 164 b and 164 c, while the siliconsemiconductor film 166 has a channel region 166 a, source/drain regions166 b and 166 c, and low-concentration impurity regions (LDD) 166 d and166 e. Compared with the channel regions 164 a and 166 a, thesource/drain regions 164 b, 164 c, 166 b, and 166 c have a higherimpurity concentration, and therefore, conductivity thereof is high. Asthe impurities, an element imparting p-type conductivity, such as boronand aluminum, and an element imparting n-type conductivity, such asphosphor and nitrogen, are represented. In the example shown in FIG. 8,the silicon semiconductor film 164 is doped with an element impartingp-type conductivity, while the silicon semiconductor film 166 is dopedwith an element imparting n-type conductivity.

The first transistor 102 has a structure which is the same as that ofthe first transistor 102 described in the First Embodiment, and the gateelectrode 108 thereof is located over the second gate insulating film168. Therefore, the second gate electrode 170 and the third gateelectrode 172 exist in the same layer as the gate electrode 108.

The gate insulating film 110 of the first transistor 102 extends so asto cover the second gate electrode 170 and the third gate electrode 172.Similarly, the interlayer film 120 extends so as to cover the secondgate electrode 170 and the third gate electrode 172. The gate insulatingfilm 110 and the interlayer film 120 also function as a film to protectthe second transistor 160 and the third transistor 162.

The second transistor 160 further possesses source/drain electrodes 180and 182, and the third transistor 162 further has source/drainelectrodes 184 and 186. As described below, these electrodes can beformed simultaneously with the first terminal 128 and the secondterminal 130 of the first transistor 102, and therefore can exist in thesame layer. Although not shown, one of the source/drain electrodes 180and 182 may be electrically connected to one of the source/drainelectrodes 184 and 186 to form a complementary metal oxide semiconductor(CMOS) transistor from the second transistor 160 and the thirdtransistor 162.

Similar to the First Embodiment, the interlayer film 120 has the firstregions 140. The first regions 140 are also included in the secondtransistor 160 and the third transistor 162 and provided so as tosurround the source/drain electrodes 180, 182, 184, and 186 as shown inFIG. 8. The first regions 140 have a higher oxygen composition thananother region of the second film 124.

Similar to the First Embodiment, the semiconductor device 300 may havethe leveling film 132 as an optional structure.

2. Manufacturing Method

A manufacturing method of the semiconductor device 300 is explained withreference to FIG. 9A to FIG. 12B. Descriptions which are the same asthose of the First Embodiment may be omitted.

2-1. Undercoat

The undercoat 106 is formed over the substrate 104 (FIG. 9A). Theundercoat 106 can be formed with the method described in the FirstEmbodiment. In the present embodiment, the undercoat 106 has a structurein which three layers are stacked as shown in FIG. 8 and FIG. 9A and maycontain the material described in the First Embodiment as appropriate.For example, the undercoat 106 may have a structure in which a filmcontaining silicon oxide, a film containing silicon nitride, and a filmcontaining silicon oxide are stacked in this order from a side of thesubstrate 104.

2-2. Silicon Semiconductor Film

Next, the silicon semiconductor films 164 and 166 are formed over theundercoat 106. There is no limitation to crystallinity of the siliconsemiconductor films 164 and 166. When a polycrystalline morphology isemployed, for example, amorphous silicon (a-Si) with a thickness ofapproximately 50 nm to 100 nm is formed with a CVD method, and a heattreatment or irradiation of light such as a laser is conducted tocrystalize a-Si. The crystallization may be carried out in the presenceof a catalyst such as nickel.

2-3. Second Gate Insulating Film

Next, the second gate insulating film 168 is formed so as to cover thesilicon semiconductor films 164 and 166 (FIG. 9B). The second gateinsulating film 168 can be formed by applying the material and themethod similar to those of the gate insulating film 110. For example,the second gate insulating film 168 can be formed with a CVD method byusing an alkoxysilane such as tetraethoxysilane as a raw material.

2-4. Gate Electrode, Second Gate Electrode, and Third Gate Electrode

Next, the gate electrode 108 is formed over the second gate insulatingfilm 168. Simultaneously, the second gate electrode 170 and the thirdgate electrode 172 are formed so as to overlap with the siliconsemiconductor films 164 and 166 (FIG. 9B). Therefore, these gateelectrodes exist in the same layer. These gate electrodes can be formedby using the material and the formation method applicable to the gateelectrode 108 described in the First Embodiment.

After that, an ion-implantation treatment or an ion-doping treatment isperformed on the silicon semiconductor films 164 and 166 from over thesubstrate 104 by using the second gate electrode 170 and the third gateelectrode 172 as a mask. In the semiconductor device 300 of the presentembodiment, the silicon semiconductor film 164 is doped with ionsimparting p-type conductivity, by which the source/drain regions 164 band 164 c are formed in the regions of the silicon semiconductor film164 which do not overlap with the second gate electrode 170, and thechannel region 164 a which is not substantially doped with ions issimultaneously formed (FIG. 9C) On the other hand, the siliconsemiconductor film 166 is doped with ions imparting n-type conductivity,by which the source/drain regions 166 b and 166 c are formed in theregions of the silicon semiconductor film 166 which do not overlap withthe third gate electrode 172, and the channel region 166 a which is notsubstantially doped with ions is simultaneously formed (FIG. 9C)

As shown in FIG. 9C, when the LDD 166 d and 166 e are arranged betweenthe source/drain regions 166 b and the channel region 166 a and betweenthe source/drain regions 166 c and the channel region 166 a of thesilicon semiconductor film 166, the LDD 166 d and 166 e can be formed byforming an insulating film on a side surface of the third gate electrode172 and performing ion doping therethrough, for example. The doped ionsmay be activated by conducting a heat treatment after the ion-doping.

2-5. Gate Insulating Film

Next, the gate insulating film 110 of the first transistor 102 is formedover the gate electrode 108 (FIG. 10A). At this time, the gateinsulating film 110 is formed so as to cover not only the gate electrode108 but also the second gate electrode 170 and the third gate electrode172. The material and the formation method described in the FirstEmbodiment can be adopted to those of the gate insulating film 110. Forexample, a single-layer film of silicon oxide or a film containing afilm including silicon nitride and a film including silicon oxide arestacked from the side of the substrate 104.

2-6. Oxide Semiconductor Film

Next, the oxide semiconductor film 112 is formed over the gateinsulating film 110 so as to overlap with the gate electrode 108 (FIG.10B). The formation method is the same as that described in the FirstEmbodiment.

Next, the source/drain electrodes 114 and 116 are formed over the oxidesemiconductor film 112 by applying the material, structure, and methoddescribed in the First Embodiment (FIG. 100).

2-8. Interlayer Film

Next, the interlayer film 120 is formed over the source/drain electrodes114 and 116 by applying the material, structure, and method described inthe First Embodiment (FIG. 11A). The interlayer film 120 is formed so asto cover the first transistor 102, the second transistor 160, and thethird transistor 162. Similar to the First Embodiment, the interlayerfilm 120 possesses the first film 122, the second film 124, and thethird film 126, and it is preferred that the first film 122 and thethird film 126 include silicon oxide, and the second film 124 includesilicon nitride. In this case, silicon oxide preferably has a smallhydrogen composition and an oxygen composition close to or larger thanthat of stoichiometry.

Next, the opening portions 118 exposing the source/drain electrode 114and 116 and opening portions 190 (second opening portions) exposing thesource/drain regions 164 b, 164 c, 166 b, and 166 c are formed in theinterlayer film 120 and the gate insulating film 110 (FIG. 11B). Theopening portions 118 and 190 can be formed by conducting plasma etchingin a gas including a fluorine-containing hydrocarbon, for example. Theopening portions 118 and the opening portions 190 can be formedindividually. However, simultaneous formation allows a reduction in thenumber of processes.

After forming the opening portions 118 and 190, the oxidative treatmentis performed in order to oxidize a part of the insulating film 120 (FIG.11B). The oxidative treatment may be carried out by applying the methoddescribed in the First Embodiment. With this process, the first regions140 are formed in the second film 124 (FIG. 12A). The oxygen compositionof these first regions 140 is higher than that of another region of thesecond film 124. In this case, the first regions 140 are exposed notonly in the opening portions 118 but also in the opening portions 190.In other words, the first regions 140 having a higher oxygen compositionstructure form the side surfaces of the opening portions 118 and 190 andare formed so as to surround the opening portions 118 and 190.

The oxidative treatment oxidizes the surfaces of the source/drainregions 164 b, 164 c, 166 b, and 166 c, resulting in thin oxide films.The oxide films are also formed on the source/drain electrodes 114 and116 depending on the material used. If the thin oxide films are notremoved, large contact resistance is caused between the first terminal128 and the second terminal 130 formed later and the source/drainelectrodes 180, 182, 184, and 186. Thus, an acid treatment is performedon the surfaces of the semiconductor films 164 and 166 in order toremove the oxide films.

As described in the First Embodiment, a preferred embodiment is to formthe second film 124 containing silicon nitride at a relatively lowtemperature under the conditions giving a small hydrogen compositionthereof. Such a film is relatively less resistive to an acid and isreadily lost or damaged.

However, as described above, the oxidative treatment is performed on theinterlayer film 120 to allow the oxidation to proceed from the surfaceof the second film 124, by which the oxygen composition of the film isincreased, the chemical stability is improved, and resistivity to anacid is remarkably enhanced. As a result, the loss of the interlayerfilm 120 and deterioration of the function thereof can be avoided, andthe semiconductor device 300 with excellent electrical properties can besupplied.

2-9. Terminal and Source/Drain Electrode

Next, the first terminal 128, the second terminal 130, the source/drainelectrodes 180, 182, 184, and 186 are formed so as to fill the openingportions 118 and 190 and to be electrically connected to thesource/drain electrodes 114 and 116 and the source/drain regions 164 b,164 c, 166 b, and 166 c (FIG. 12B). These terminals and electrodes canbe simultaneously formed by applying the material and the methoddescribed in the First Embodiment. Therefore, the first terminal 128,the second terminal 130, and the source/drain electrodes 180, 182, 184,and 186 can exist in the same layer.

2-10. Leveling Film

Similar to the First Embodiment, the leveling film 132 is formed as anoptional structure (FIG. 12B). The formation method is as described inthe First Embodiment.

Through these processes, the semiconductor device 300 can be fabricated.

The semiconductor device 300 of the present embodiment possesses, overthe substrate 104, a plurality of transistors (first transistor 102,second transistor 160, and third transistor 162) which are different inmaterial of the semiconductor films governing the electrical properties.The second film 124 which has a function to prevent entrance ofimpurities but has low chemical stability is included in the interlayerfilm 120 formed over the first transistor 102 containing the oxidesemiconductor film 112. However, the oxidative treatment on the secondfilm 124 is capable of improving chemical stability, while leaving thefunction to prevent entrance of impurities. As a result, the firsttransistor 102 with small variation and excellent electrical propertiescan be obtained.

The first transistor 102 including the oxide semiconductor 112 ischaracterized by a low off-current. On the other hand, the secondtransistor 160 and the third transistor 162 having the siliconsemiconductor films 164 and 166 are characterized by high field-effectmobility. The application of the present embodiment enables productionof a semiconductor device having these features.

Fourth Embodiment

In the present embodiment, a display device including the semiconductordevice 100, 200, or 300 described in the First to Third Embodiments anda manufacturing method thereof are explained by using FIG. 13 to FIG.15. Explanation of duplicated contents of the First to Third Embodimentsmay be omitted.

1. Outline Structure

A schematic top view of a display device 400 of the present embodimentis shown in FIG. 13. The display device 400 has a display region 206provided with a plurality of pixels 204 and gate side driver circuits(hereinafter, referred to as driver circuits) 208 over one surface (topsurface) of the substrate 104. Display elements such as a light-emittingelement and a liquid crystal element giving colors different from oneanother can be disposed in the plurality of pixels 204, by whichfull-color display can be conducted. For example, display elementsproviding red, green, and blue colors may be arranged in three pixels204, respectively. Alternatively, display elements exhibiting whitecolor may be used in all pixels 204, and full-color display may beperformed by using a color filter to extract red, green, or blue colorsfrom the respective pixels 204. The colors finally extracted are notlimited to a combination of red, green, and blue colors. For instance,four kinds of colors of red, green, blue, and white may be respectivelyextracted from four pixels 204. The arrangement of the pixels 204 isalso not limited, and a stripe arrangement, a delta arrangement, aPentile arrangement, and the like can be employed.

Wirings 210 extend from the display region 206 to a side surface of thesubstrate 104 (a short side of the display device 400 in FIG. 13), andthe wirings 210 are exposed at an edge portion of the substrate 104 toform terminals 212. The terminals 212 are connected to a connector (notshown) such as a flexible printed circuit (FPC). The display region 206is also electrically connected to an IC chip 214 via the wirings 210.With this structure, image signals supplied from an external circuit(not shown) are provided to the pixels 204 through the driver circuits208 and the IC chip 214, and the display elements of the pixels 204 arecontrolled, allowing an image to be reproduced on the display region206. Although not shown, the display device 400 may have a source sidedriver circuit at a periphery of the display region 206 instead of theIC chip 214. In the present embodiment, two driver circuits 208 aredisposed so as to sandwich the display region 206. However, a singlenumber of driver circuits 208 may be employed. Furthermore, the drivercircuits 208 may not be arranged over the substrate 104, and a drivercircuit 208 fabricated over another substrate may be mounted on theconnector.

2. Pixel Circuit

An example of equivalent circuits of the pixels 204 is shown in FIG. 14.In FIG. 14, an example including a light-emitting element 238 such as anorganic electroluminescence element as a display element 236 isillustrated. The pixel 204 possesses a gate line 220, a signal line 222,a current-supplying line 224, and a power source line 226.

The pixel 204 has a switching transistor 230, a driving transistor 232,a storage capacitor 234, and the display element 236. A gate, a source,and a drain of the switching transistor 230 are electrically connectedto the gate line 220, the signal line 222, and a gate of the drivingtransistor 232, respectively. A source of the driving transistor 232 iselectrically connected to the current-supplying line 224. One electrodeof the storage capacitor 234 is electrically connected to the drain ofthe switching transistor 232 and the gate of the driving transistor 232,and the other electrode is electrically connected to a drain of thedriving transistor 232 and one electrode (first electrode) of thedisplay element 236. The other electrode (second electrode) of thedisplay element 236 is electrically connected to the power source line226. Note that the source and drain of each transistor may beinterchanged depending on a direction of a current flow and polarity ofthe transistor.

In FIG. 14, a structure is illustrated in which the pixel 204 possessestwo transistors (switching transistor 230 and driving transistor 232)and one storage capacitor (storage capacitor 234). However, the displaydevice of the present embodiment is not limited to this structure, andthe number of the transistors may be one, three, or more. The pixel 204may not include a storage capacitor or possess a plurality of storagecapacitors. Furthermore, the display element 236 is not limited to alight-emitting element and may be a liquid crystal element or anelectrophoresis element. The wirings are not limited to theaforementioned gate line 220, signal line 222, current supplying line224, and power source line 226. For example, the pixel 204 may have aplurality of gate lines or a wiring having another function.Alternatively, at least one of these wirings may be shared by theplurality of pixels 204.

3. Cross-Sectional Structure

A schematic cross-sectional view of the display device 400 is shown inFIG. 15. FIG. 15 schematically shows the structure of one pixel 204 inthe display region 206. The display device 400 has a part of thesemiconductor device 300 described in the Third Embodiment. Here, thefirst transistor 102 and the second transistor 160 of the semiconductordevice 300 are included in the pixel 204. The former corresponds to theswitching transistor 230, and the latter corresponds to the drivingtransistor 232 in FIG. 14. Thus, although not shown, one of thesource/drain electrodes 114 and 116 of the first transistor 102 isconnected to the second gate electrode 170 of the second transistor 160.

The display device 400 has the leveling film 132, and the leveling film132 possesses an opening portion reaching the source/drain electrode 180of the second transistor 160. The display device 400 further has aconnection electrode 240 covering a side surface of the opening portionand electrically connected to the source/drain electrode 180. Theconnection electrode 240 may be formed with a conductive oxide having alight-transmitting property, such as indium-tin oxide (ITO) andindium-zinc oxide (IZO), by applying a sputtering method and the like,for example. The connection electrode 240 is not necessarily disposed.However, formation of the connection electrode 240 allows thesource/drain electrodes 180 of the second transistor 160 to be protectedby which an increase in contact resistance can be avoided.

The display device 400 further possesses an insulating film 242 coveringa side surface of the connection electrode 240 and a top surface of theleveling film 132. The insulating film 242 can include an inorganicmaterial containing silicon and can be formed by using a sputteringmethod, a CVD method, and the like. The connection electrode 240 isexposed from the insulating film 242 in the opening portion of theleveling film 132 in which the connection electrode 240 is connected tothe first electrode 250 of the display element 238. Here, as shown inFIG. 15, the insulating film 242 has an opening portion 244 over theleveling film 132 in which a partition wall 256 formed later contactswith the leveling film 132. This opening portion 244 functions totransport impurities (water and gas such as oxygen) eliminated from theleveling film 132 to a side of the partition wall 256.

The display device 400 has the light-emitting element 238 over theleveling film 132. The first electrode 250 of the light-emitting element238 is electrically connected to the source/drain electrode 180 throughthe connection electrode 240 in the opening portion provided in theleveling film 132.

When light emission from the light-emitting element 238 is extractedthrough the substrate 104, a material with a light-transmitting propertyexemplified by a conductive oxide such as ITO and IZO can be used forthe first electrode 250. On the other hand, when the light emission fromthe light-emitting element 238 is extracted from an opposite side to thesubstrate 104, a metal such as aluminum and silver or an alloy thereofcan be used. Alternatively, a stacked layer of the aforementioned metalor alloy with the conductive oxide, such as a stacked structure in whichthe metal is sandwiched by the conductive oxide (e.g., ITO/silver/ITOetc.) may be employed.

The partition wall 256 is arranged so as to cover an edge portion of thefirst electrode 250 and the opening portion provided in the levelingfilm 132 and has a function to absorb steps caused by these elements andelectrically insulate the first electrodes 250 of the adjacent pixels240 from each other. The partition wall 256 is also called a bank (rib).The partition wall 256 can be formed with a material usable in theleveling film 132, such as an epoxy resin and an acrylic resin. Thepartition wall 256 has an opening portion to expose a part of the firstelectrode 250, and an edge of the opening portion preferably has amoderately tapered shape. A steep inclination of the opening portionreadily causes a coverage defect in an EL layer 250 and the secondelectrode 254 formed later.

The light-emitting element 238 has the EL layer 252, and the EL layer252 is formed so as to cover the first electrode 250 and the partitionwall 256. In the present specification and the claims, an EL layer meansall of the layers sandwiched by a pair of electrodes and may be formedwith a single layer or a plurality of layers. For example, the EL layer252 may be formed by appropriately combining a carrier-injection layer,a carrier-transporting layer, an emission layer, a carrier-blockinglayer, an exciton-blocking layer, and the like. Furthermore, thestructure of the EL layer 252 may be different between the adjacentpixels 204. For example, the EL layer 252 may be configured so that theemission layer is different but other layers have the same structurebetween the adjacent pixels 204 and, by which different emission colorscan be obtained from the adjacent pixels 204 to enable full-colordisplay. On the contrary, the same EL layer 250 may be used in allpixels 204. In this case, the white-emissive EL layer 252 is formed soas to be shared by all pixels 204, and a wavelength of light extractedfrom each pixel 204 is selected by using a color filter and the like.The EL layer 250 can be formed by applying an evaporation method or theaforementioned wet-type film-formation method.

The light-emitting element 238 has the second electrode 254 over the ELlayer 252. The light-emitting element 238 is configured by the firstelectrode 250, the EL layer 250, and the second electrode 254. Carriers(holes and electrons) are injected into the EL layer 252 from the firstelectrode 250 and the second electrode 254, and the light-emission isobtained through a relaxation process of an excited state generated byrecombination of the carriers to a ground state. Hence, a region of thelight-emitting element 238 in which the EL layer 252 and the firstelectrode 250 are in direct contact with each other is an emissionregion.

When the light-emission from the light-emitting element 238 is extractedthrough the substrate 104, a metal such as aluminum and silver or analloy thereof can be used for the second electrode 254. On the otherhand, when the light-emission from the light-emitting element 238 isextracted through the second electrode 254, the second electrode 254 isformed by using the aforementioned metal or alloy so as to have athickness which allows visible light to pass therethrough.Alternatively, a material having a light-transmitting propertyexemplified by a conductive oxide such as ITO and IZO can be used forthe second electrode 254. Moreover, a stacked structure of theaforementioned metal or alloy with the conductive oxide (e.g., Mg—Ag/ITOetc.) may be employed in the second electrode 254. The second electrode254 can be formed with an evaporation method, a sputtering method, andthe like.

A passivation film (sealing film) 260 is provided over the secondelectrode 254. A function of the passivation film 260 is to preventmoisture from entering the precedingly fabricated light-emitting element238 from outside, and the passivation film 260 preferably has a highgas-barrier property. For example, it is preferred to form thepassivation film 260 by using an inorganic material such as siliconnitride, silicon oxide, silicon nitride oxide, and silicon oxynitride.Alternatively, an organic resin including an acrylic resin, apolysiloxane, a polyimide, a polyester, and the like may be used. In thestructure illustratively shown in FIG. 15, the passivation film 260possesses a three-layer structure including a first layer 262, a secondlayer 264, and a third layer 266.

Specifically, the first layer 262 may include an inorganic insulatorsuch as silicon oxide, silicon nitride, silicon oxynitride, and siliconnitride oxide and may be formed by applying a CVD method or a sputteringmethod. A polymer material can be employed for the second layer 264, forexample, and can be selected from an epoxy resin, an acrylic resin, apolyimide, a polyester, a polycarbonate, a polysiloxane, and the like.The second layer 264 can be formed with the aforementioned wet-typefilm-formation method. The second layer 264 may also be formed bygasifying or atomizing oligomers serving as a raw material of theaforementioned polymer material and spraying the first layer 262 withthe oligomers, followed by polymerizing the oligomers. In this case, apolymerization initiator may be mixed in the oligomers. Additionally,the first layer 262 may be sprayed with the oligomers while cooling thesubstrate 104. The third layer 266 can be formed by employing thematerial and the formation method which are the same as those of thefirst layer 262.

Although not shown, an opposing substrate may be disposed over thepassivation film 260 as an optional structure. The opposing substrate isfixed with the substrate 104 by using an adhesive. In this case, a spacebetween the opposing substrate and the passivation film may be filledwith an inert gas or a filler such as a resin. Alternatively, thepassivation film 260 and the opposing substrate may be adhered directlywith an adhesive. When a filler is used, the filler preferably has ahigh light-transmitting property. When the opposing substrate is fixedto the substrate 104, a gap therebetween may be adjusted by including aspacer in an adhesive or a filler. Alternatively, a structural memberserving as a spacer may be placed between the pixels 204.

The opposing substrate may be further provided with a light-shieldingfilm having an opening in a region overlapping with the emission regionor a color filter over a region overlapping with the emission region.The light-shielding film is formed by using a metal with a relativelylow reflectance, such as chromium and molybdenum, or a resin materialincluding a coloring material of black or a similar color and has afunction to block scattered light, reflected ambient light, and the likeother than the light directly obtained from the emission region. Anoptical property of the color filter may be changed between the adjacentpixels 204 and may be configured to extract red, green, and blueemissions, for example. The light-shielding film and the color filtermay be provided to the opposing substrate with a base film interposedtherebetween, and an overcoat layer may be further arranged so as tocover the light-shielding film and the color filter.

The display device 400 shown in the present embodiment has the secondtransistor 160 including a silicon semiconductor film as the drivingtransistor 232. A transistor including a silicon semiconductor,particularly, a transistor including a polycrystalline siliconsemiconductor has a high filed-effect mobility, which allows a largecurrent to be flowed therein. Therefore, it is possible to supply alarge current to the light-emitting element 238.

On the other hand, the use of the first transistor 102 as the switchingtransistor 230 allows the image data transmitted from the signal line222 to be stored at the second gate electrode 170 of the secondtransistor 160 serving as the driving transistor 232 or at the storagecapacitor 234 for a long time because a transistor including an oxidesemiconductor exhibits a low off-current. Hence, the storage capacitor234 becomes unnecessary, or its size can be decreased. As a result, itis possible to decrease power consumption and increase an aperture ratioof the display device 400. Additionally, variation of a current flowingin the light-emitting element 238 can be reduced because a transistorincluding an oxide semiconductor has small variation in thresholdvoltage. Accordingly, the display device 400 capable of supplying ahigh-quality image can be produced.

Fifth Embodiment

In the present embodiment, a display device including the semiconductordevice 100, 200, or 300 described in the First to Third Embodiments anda manufacturing method thereof are explained by using FIG. 13, FIG. 14,and FIG. 16. Explanation of duplicated contents of the First to FourthEmbodiments may be omitted.

A schematic cross-sectional view of a display device 500 of the presentembodiment is shown in FIG. 16. FIG. 16 corresponds to thecross-sectional view of the pixel 204 shown in FIG. 13. The displaydevice 500 has a part of the semiconductor device 300 described in theThird Embodiment in the pixel 204, and the source/drain electrode 116 ofthe first transistor 102 is electrically connected to the light-emittingelement 238. That is, the first transistor 102 functions as the drivingtransistor 232 in the pixel 204 shown in FIG. 14. Moreover, the secondtransistor 160 corresponds to the switching transistor 230. Although notshown in FIG. 16, one of the source/drain electrodes 180 and 182 of thesecond transistor 160 is electrically connected to the gate electrode108 of the first transistor 102.

The display device 500 shown in the present embodiment has the secondtransistor 160 including a silicon semiconductor film as the switchingtransistor 230. Since a transistor including a silicon semiconductorfilm, particularly, a transistor including a polycrystalline silicontransistor has a high filed-effect mobility, a high-speed switchingcharacteristic is attainable in the pixel 204.

On the other hand, the pixel 204 has the first transistor 102 includingthe oxide semiconductor film 112 as the driving transistor 232. Since atransistor including an oxide semiconductor film has small variation inthreshold voltage, it is possible to reduce variation in current flowingin the light-emitting element 238. As a result, the display device 500capable of supplying a high-quality image can be produced.

Sixth Embodiment

In the present embodiment, a display device including the semiconductordevice 100, 200, or 300 described in the First to Third Embodiments anda manufacturing method thereof are explained by using FIG. 13, FIG. 14,and FIG. 17. Explanation of duplicated contents of the First to FifthEmbodiments may be omitted.

A schematic cross-sectional view of a display device 600 of the presentembodiment is shown in FIG. 17. FIG. 17 schematically shows one pixel204 located in the display region 206 and closest to the driver circuit208, a part of the driver circuit 208, and a peripheral structurethereof. The display device 600 has the semiconductor device 300described in the Third Embodiment. Here, the first transistor 102 of thesemiconductor device 300 is included in the pixel 204 and functions asthe switching transistor 230 shown in FIG. 14. On the other hand, thesecond transistor 160 and the third transistor 162 are included in thedriver circuit 208.

In a region including the driver circuit 208, the power source line 226is provided over the leveling film 132. The power source line 226 cancontain a conductive oxide having a light-transmitting property, such asITO and IZO, a metal such as aluminum, or an alloy thereof and can beformed simultaneously with the first electrode 252 of the light-emittingelement 238 or the connection electrode 240 described in the FourthEmbodiment. An edge portion of the power source line 226 is covered bythe partition wall 256, and a portion exposed from the partition wall256 is connected to the second electrode 254 extending from thelight-emitting element 238. This structure allows the second electrode254 to be supplied with a constant voltage applied to the power sourceline 226.

An auxiliary electrode 228 is formed so as to be in contact with thepower source line 226. The auxiliary electrode 228 is covered by thepartition wall 256. The auxiliary electrode 228 can include a metal suchas aluminum and molybdenum or an alloy thereof and has a function tocompensate the low conductivity of the power source 226. When theresistance of the second electrode 254 is relatively high, the formationof the auxiliary electrode 228 prevents a voltage drop caused by thesecond electrode 254. Therefore, the auxiliary electrode 228 may not beprovided when the power source line 226 has a sufficient conductivity.

The display device 600 shown in the present embodiment possesses thesecond transistor 160 and the third transistor 162 each including asilicon semiconductor film in the driver circuit 208. Since a transistorincluding a silicon semiconductor film, particularly, a transistorincluding a polycrystalline silicon transistor has a high filed-effectmobility, a high-speed operation is feasible in the driving circuit 208including these transistors. On the other hand, the pixel 204 has thefirst transistor 102 including the oxide semiconductor film 112. Since atransistor including an oxide semiconductor film has a low off-current,the image data transmitted from the signal line 222 can be stored at thegate of the driving transistor 232 or at the storage capacitor 234 for along time. Hence, the storage capacitor 234 becomes unnecessary, or itssize can be decreased. As a result, it is possible to decrease powerconsumption and increase an aperture ratio of the display device 600.Additionally, variation of a current flowing in the light-emittingelement 238 can be reduced because a transistor including an oxidesemiconductor has small variation in threshold voltage. Accordingly, thedisplay device 600 capable of supplying a high-quality image can beproduced.

Seventh Embodiment

In the present embodiment, a display device including the semiconductordevice 100, 200, or 300 described in the First to Third Embodiments anda manufacturing method thereof are explained by using FIG. 13 and FIG.18. Explanation of duplicated contents of the First to Sixth Embodimentsmay be omitted.

A schematic cross-sectional view of a display device 700 of the presentembodiment is shown in FIG. 18. FIG. 18 schematically shows the pixel204 in the display region 206 shown in FIG. 13 and a part of the drivercircuit 208. The display device 700 has the semiconductor device 300described in the Third Embodiment. The first transistor 102 includingthe oxide semiconductor film 112 is disposed in the pixel 204, while thesecond transistor 160 and the third transistor 162 respectivelyincluding the silicon semiconductor films 164 and 166 are provided inthe driver circuit 208.

Unlike the display devices 400, 500, and 600, the display device 700possesses a liquid crystal element 302 as a display element in the pixel204. The liquid crystal element 302 has a first electrode 304 over theleveling film 132, a first orientation film 306 over the first electrode304, a liquid crystal layer 308 over the first orientation film 306, asecond orientation film 310 over the liquid crystal layer 308, and asecond electrode 312 over the second orientation film 310. A colorfilter 314 is provided over the liquid crystal element 302 as anoptional structure. A light-shielding film 316 is formed in a regionoverlapping with the driver circuit 208.

An opposing substrate 318 is disposed over the liquid crystal element302 and is fixed to the substrate 104 with a sealing material 320. Theliquid crystal layer 308 is sandwiched between the substrate 104 and theopposing substrate 318, and a thickness of the liquid crystal layer 308,that is, a distance between the substrate 104 and the opposing substrate318 is maintained with a spacer 322. Although not shown, a polarizationplate, a retardation film, or the like may be arranged under thesubstrate 104 or over the opposing substrate 318.

In the present embodiment, the display device 700 is explained so as tohave the so-called VA (Vertical Alignment) mode or TN (Twisted Nematic)mode. However, the liquid crystal element 302 is not limited to thesemodes and may have another mode such as IPS (In-Plan-Switching) mode.When a transmissive liquid crystal element is utilized, the liquidcrystal element 302 is arranged so as not to overlap with the firsttransistor 102.

The display device 700 shown in the present embodiment possesses thesecond transistor 160 and the third transistor 162 each including asilicon semiconductor film in the driver circuit 208. Since a transistorincluding a silicon semiconductor film, particularly, a transistorincluding a polycrystalline silicon transistor has a high filed-effectmobility, a high-speed operation is feasible in the driving circuit 208including these transistors. On the other hand, the pixel 204 has thefirst transistor 102 including the oxide semiconductor film 112. Since atransistor including an oxide semiconductor has small variation inthreshold voltage, variation of a voltage applied to the liquid crystalelement 302 can be reduced. Accordingly, variation of transmittance ofthe liquid crystal element 302 is decreased, and the display device 700capable of supplying a high-quality image can be produced.

The aforementioned modes described as the embodiments of the presentinvention can be implemented by appropriately combining with each otheras long as no contradiction is caused. Furthermore, any mode which isrealized by persons ordinarily skilled in the art through theappropriate addition, deletion, or design change of elements or throughthe addition, deletion, or condition change of a process is included inthe scope of the present invention as long as they possess the conceptof the present invention.

In the specification, although the cases of the organic EL displaydevice are exemplified, the embodiments can be applied to any kind ofdisplay devices of the flat panel type such as other self-emission typedisplay devices, liquid crystal display devices, and electronic papertype display device having electrophoretic elements and the like. Inaddition, it is apparent that the size of the display device is notlimited, and the embodiment can be applied to display devices having anysize from medium to large.

It is properly understood that another effect different from thatprovided by the modes of the aforementioned embodiments is achieved bythe present invention if the effect is obvious from the description inthe specification or readily conceived by persons ordinarily skilled inthe art.

What is claimed is:
 1. A semiconductor device comprising: a firsttransistor over a substrate, the first transistor comprising: a gateelectrode; an oxide semiconductor film; and a gate insulating filmbetween the gate electrode and the oxide semiconductor film; aninsulating film over the first transistor, the insulating filmcomprising a first film and a second film over the first film; and aterminal electrically connected to the oxide semiconductor film throughan opening portion in the insulating film, wherein the insulating filmhas a first region in contact with the terminal, and an oxygencomposition of the first region is larger than that of another region ofthe insulating film.
 2. The semiconductor device according to claim 1,wherein the oxygen composition of the first region decreases withincreasing distance from an interface with the terminal.
 3. Thesemiconductor device according to claim 1, wherein the oxygencomposition of the first region decreases with increasing distance froman interface with the terminal in a direction parallel to a surface ofthe substrate.
 4. The semiconductor device according to claim 1, whereinthe first film includes silicon and oxygen, the second film includessilicon and nitrogen, and the first region is included in the secondfilm.
 5. The semiconductor device according to claim 4, wherein theinsulating film further comprises a third film over the second film, thethird film including silicon and oxygen.
 6. A display device comprising:a first transistor over a substrate, the first transistor comprising: agate electrode; an oxide semiconductor film; and a gate insulating filmbetween the gate electrode and the oxide semiconductor film; aninsulating film over the first transistor, the insulating filmcomprising a first film and a second film over the first film; aterminal electrically connected to the oxide semiconductor film throughan opening portion in the insulating film; a leveling film over theterminal; and a display element over the leveling film, wherein theinsulating film has a first region in contact with the terminal, and anoxygen composition of the first region is larger than that of anotherregion of the insulating film.
 7. The display device according to claim6, wherein the oxygen composition of the first region decreases withincreasing distance from an interface with the terminal.
 8. The displaydevice according to claim 6, wherein the display element is electricallyconnected to the terminal.
 9. The display device according to claim 6,further comprising: a second transistor comprising: a semiconductor filmincluding silicon; a gate electrode; and a gate insulating film betweenthe semiconductor film and the gate electrode; wherein the gateelectrode of the second transistor is electrically connected to thefirst transistor, and the display element is electrically connected tothe second transistor.
 10. The display device according to claim 6,comprising: a display region and a driver circuit region, wherein thefirst transistor is included in the display region, and the drivercircuit region comprises a second transistor comprising: a semiconductorfilm including silicon; a gate electrode; and a gate insulating filmbetween the semiconductor film and the gate electrode.
 11. The displaydevice according to claim 6, wherein the oxygen composition of the firstregion decreases with increasing distance from an interface with theterminal in a direction parallel to a surface of the substrate.
 12. Thedisplay device according to claim 6, wherein the first film includessilicon and oxygen, the second film includes silicon and nitrogen, andthe first region is included in the second film.
 13. The display deviceaccording to claim 12, wherein the insulating film further comprises athird film over the second film, the third film including silicon andoxygen.
 14. A manufacturing method of a semiconductor device, themanufacturing method comprising: forming a first transistor over asubstrate, the first transistor comprising: a gate electrode; an oxidesemiconductor film; and a gate insulating film between the gateelectrode and the oxide semiconductor film; forming an insulating filmcomprising a first film and a second film over the first film; formingan opening portion in the insulating film; oxidizing the insulating filmso that a surface portion of the opening portion has a first region withan oxygen composition larger than that in another region; and forming aterminal in the opening portion so as to be electrically connected tothe oxide semiconductor film.
 15. The manufacturing method according toclaim 14, wherein the oxidation is performed so that the oxygencomposition of the first region decreases with increasing distance froman interface with the terminal.
 16. The manufacturing method accordingto claim 14, wherein the oxidation is performed so that the first regionis in contact with a side surface of the opening portion.
 17. Themanufacturing method according to claim 14, further comprising: forminga second transistor comprising a semiconductor film including siliconbefore forming the first transistor, wherein the insulating film isformed so as to cover the second transistor; forming a second openingportion exposing the semiconductor film simultaneously with theformation of the opening portion; and treating a surface of thesemiconductor film with a solution including hydrogen fluoride after theoxidization and before the formation of the terminal.
 18. Themanufacturing method according to claim 17, wherein the secondtransistor comprises a second gate electrode, and the second gateelectrode is formed simultaneously with the gate electrode.
 19. Themanufacturing method according to claim 14, wherein the first filmincludes silicon and oxygen, the second film includes silicon andnitrogen, and the first region is included in the second film.
 20. Themanufacturing method according to claim 19, wherein the insulating filmfurther comprises a third film over the second film, the third filmincluding silicon and oxygen.